Porous carbon having connecting mesopores and electrode

ABSTRACT

To provide a non-aqueous electrolyte electricity-storage element including a positive electrode including a positive-electrode active material capable of inserting and releasing anions, a negative electrode including a negative-electrode active material capable of inserting and releasing cations, and a non-aqueous electrolyte, wherein the positive-electrode active material is porous carbon having pores having a three-dimensional network structure, and wherein a changing rate of a cross-sectional thickness of a positive electrode film including the positive-electrode active material defined by Formula (1) below is less than 45%.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 15/683,908 filed Aug. 23, 2017, which in turn is acontinuation application of International Application No.PCT/JP2016/053291, filed Feb. 3, 2016, which claims priority to JapanesePatent Application No. 2015-048263, filed Mar. 11, 2015. The contents ofthese applications are incorporated herein by reference in theirentirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present disclosure relates to a non-aqueous electrolyteelectricity-storage element.

Description of the Related Art

In recent years, properties of non-aqueous electrolyteelectricity-storage elements having high energy densities have beenimproved and the non-aqueous electrolyte electricity-storage elementshave been widely used to correspond to reduction in sizes andimprovements in performances of mobile devices. Moreover, developmentsof non-aqueous electrolyte electricity-storage elements having thelarger capacities and having excellent safety have been conducted and ithas been started that the above-described non-aqueous electrolyteelectricity-storage elements are mounted in electric cars.

As the non-aqueous electrolyte electricity-storage element, variouslithium ion secondary cells are used. The lithium ion secondary cellincludes a positive electrode formed of lithium-cobalt complex oxideetc., a negative electrode formed of carbon, and a non-aqueouselectrolyte formed by dissolving a lithium salt in a non-aqueoussolvent. At the time of charging the lithium ion secondary cell, lithiuminside the positive electrode is released from the positive electrodeand inserted into the carbon of the negative electrode, and at the timeof discharging the lithium ion secondary cell, the lithium inserted intothe negative electrode is released to return to the composite oxide ofthe positive electrode, to thereby perform charge and discharge of thelithium ion secondary cell.

In a case where LiPF₆ is used as a lithium salt, as represented by thefollowing reaction formula, charge is performed by inserting PF₆ ⁻ froma non-aqueous electrolyte into a positive electrode and inserting Li⁺from the non-aqueous electrolyte into the negative electrode, anddischarge is performed by releasing PF₆ ⁻, from the positive electrodeto the non-aqueous electrolyte and releasing Li⁺ from the negativeelectrode to the non-aqueous electrolyte.

PF₆ ⁻ nC

Cn(PF₆)+e ⁻  Positive electrode

Li⁺ +nC+e ⁻

LiC_(n)  Negative electrode

-   -   charging reaction    -   discharge reaction

Known as an active material capable of inserting and releasing anionsare using black lead to insert and release anions to intercalation ofthe black lead as disclosed in Japanese Patent No. 4569126 and JapanesePatent No. 4314087, using absorption and detachment of anions to asurface of a carbon material a BET specific surface area of which isincreased to a certain degree by alkali activation as disclosed inJapanese Patent No. 5399185, and using absorption and detachment ofanions to activated carbon having a large BET specific surface area asdisclosed in Japanese Unexamined Patent Application Publication No.2012-195563. Use of black lead that can utilize insertion and release ofanions to intercalation can increase a specific capacity per a unit massof the active material.

When a highly graphitized artificial black lead or natural black leadmaterial is used as a positive-electrode active material, black leadcrystals are collapsed (cleaved) as anions are electrochemicallyaccumulated to the black lead material. Therefore, a capacity ofreversible accumulation and release of anions is decreased by repeatedlyperforming charge and discharge.

SUMMARY OF THE INVENTION

According to one aspect of the present disclosure, a non-aqueouselectrolyte electricity-storage element includes a positive electrodeincluding a positive-electrode active material capable of inserting andreleasing anions, a negative electrode including a negative-electrodeactive material capable of inserting and releasing cations, and anon-aqueous electrolyte. The positive-electrode active material isporous carbon having pores having a three-dimensional network structure.A changing rate of a cross-sectional thickness of a positive electrodefilm including the positive-electrode active material defined by Formula(1) below is less than 45%.

$\begin{matrix}{\begin{matrix}{{Changing}\mspace{14mu} {rate}\mspace{14mu} {of}} \\{{cross}\text{-}{sectional}\mspace{14mu} {thickness}\mspace{11mu} (\%)}\end{matrix} = {\frac{\begin{matrix}{{{Film}\mspace{14mu} {thickness}\mspace{14mu} {after}\mspace{14mu} {charge}\text{-}{discharge}} -} \\{{Film}\mspace{14mu} {thickness}\mspace{14mu} {before}\mspace{14mu} {charge}\text{-}{discharge}}\end{matrix}}{{Film}\mspace{14mu} {thickness}\mspace{14mu} {before}\mspace{14mu} {charge}\text{-}{discharge}} \times 100}} & {{Formula}\mspace{14mu} (1)}\end{matrix}$

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view illustrating one example of a non-aqueouselectrolyte electricity-storage element of the present disclosure;

FIG. 2 is a graph depicting charge-discharge curves of the 50th cycle,500th cycle, and 1,000th cycle of Example 1;

FIG. 3 is a graph depicting charge-discharge curves of the 50th cycle,100th cycle, and 153rd cycle of Comparative Example 1; and

FIG. 4 is a graph depicting charge-discharge curves of the 50th cycle,500th cycle, and 1,000th cycle of Comparative Example 2.

DESCRIPTION OF THE EMBODIMENTS

The present disclosure has an object to provide a non-aqueouselectrolyte electricity-storage element that maintains a high energydensity, inhibits expansion of an electrode, and has excellent cycleproperties.

According to the present disclosure, a non-aqueous electrolyteelectricity-storage element having the following properties can beprovided.

(1) Having a high energy density.(2) Capable of inhibiting expansion of a positive electrode.(3) Capable of enhancing cycle properties.

(Non-Aqueous Electrolyte Electricity-Storage Element)

A non-aqueous electrolyte electricity-storage element of the presentdisclosure includes a positive electrode including a positive-electrodeactive material capable of inserting and releasing anions, a negativeelectrode including a negative-electrode active material capable ofinserting and releasing cations, and a non-aqueous electrolyte. Thepositive-electrode active material is porous carbon having pores havinga three-dimensional network structure. A changing rate of across-sectional thickness of a positive electrode film including thepositive-electrode active material defined by Formula (1) below is lessthan 45%. The non-aqueous electrolyte electricity-storage element mayfurther include other members according to the necessity.

$\begin{matrix}{\begin{matrix}{{Changing}\mspace{14mu} {rate}\mspace{14mu} {of}} \\{{cross}\text{-}{sectional}\mspace{14mu} {thickness}\mspace{11mu} (\%)}\end{matrix} = {\frac{\begin{matrix}{{{Film}\mspace{14mu} {thickness}\mspace{14mu} {after}\mspace{14mu} {charge}\text{-}{discharge}} -} \\{{Film}\mspace{14mu} {thickness}\mspace{14mu} {before}\mspace{14mu} {charge}\text{-}{discharge}}\end{matrix}}{{Film}\mspace{14mu} {thickness}\mspace{14mu} {before}\mspace{14mu} {charge}\text{-}{discharge}} \times 100}} & {{Formula}\mspace{14mu} (1)}\end{matrix}$

The non-aqueous electrolyte electricity-storage element of the presentdisclosure has been accomplished based on the finding described below.The invention disclosed in PTL 2 is to provide an electrochemicalcapacitor that has an excellent energy density and improved cycledurability with using, as a positive-electrode active material, softcarbon subjected to an activation treatment with KOH to give fine poresat the surface. Moreover, the invention disclosed in PTL 2 is atechnology associated with an electrochemical capacitor, and usessurface adsorption of ions and therefore cleavage of the carbon does notoccur. As a BET specific surface area of the positive-electrode activematerial increases, however, decomposition of an electrolyte etc. tendsto occur. Therefore, voltage cannot be set very high, and to 4.8 V atthe highest. Moreover, accumulation of anions into the positiveelectrode cannot be utilized. Accordingly, a capacity of the capacitorcannot be sufficiently increased.

In an anion intercalation electricity-storage element, an electrodelargely expands or contracts through charge and discharge to therebychange a thickness of a positive electrode film. Then, compressionstress or tensile stress is generated within the electricity-storageelement depending on a changing rate of the film thickness of thepositive electrode, and cracking in the positive electrode material mayformed, the positive electrode material and a separator may be squashed,the positive electrode material may be peeled from a positive electrodecollector, and moreover a space may be formed between the positiveelectrode or the negative electrode and the separator, as cycles arerepeated, and as a result, a liquid shortage of a non-aqueouselectrolyte is caused to inhibit a reaction of the electricity-storageelement. Accordingly, a changing rate of a cross-sectional thickness ofthe positive electrode film affects a service life of theelectricity-storage element.

In the present disclosure, a combination of charge and discharge undercertain conditions is regarded as 1 cycle, and a changing rate of across-sectional thickness of the positive electrode film including thepositive-electrode active material before and after a charge-dischargetest performed up to 50th cycle, where the changing rate is defined byFormula (1) below, is less than 45% and is preferably 20% or less. Whenthe changing rate of the cross-sectional thickness is less than 45%,cycle properties are improved.

$\begin{matrix}{\begin{matrix}{{Changing}\mspace{14mu} {rate}\mspace{14mu} {of}} \\{{cross}\text{-}{sectional}\mspace{14mu} {thickness}\mspace{11mu} (\%)}\end{matrix} = {\frac{\begin{matrix}{{{Film}\mspace{14mu} {thickness}\mspace{14mu} {after}\mspace{14mu} {charge}\text{-}{discharge}} -} \\{{Film}\mspace{14mu} {thickness}\mspace{14mu} {before}\mspace{14mu} {charge}\text{-}{discharge}}\end{matrix}}{{Film}\mspace{14mu} {thickness}\mspace{14mu} {before}\mspace{14mu} {charge}\text{-}{discharge}} \times 100}} & {{Formula}\mspace{14mu} (1)}\end{matrix}$

However, the cross-sectional film thickness of the positive electrodefilm is an average value of a thickness measured at randomly selected 3points on the positive electrode film using, for example, a digital gage(DG-205, available from OZAKI MFG. CO., LTD.).

A discharge capacity of the non-aqueous electrolyte electricity-storageelement is preferably 50 mAh/g or greater but 140 mAh/g or less undercharge-discharge conditions of the non-aqueous electrolyteelectricity-storage element in view of both a high capacity and a cycleservice life.

<Positive Electrode>

The positive electrode is not particularly limited and may beappropriately selected depending on the intended purpose, as long as thepositive electrode includes a positive-electrode active material.Examples of the positive electrode include a positive electrode in whicha positive electrode material including a positive-electrode activematerial is disposed on a positive electrode collector.

A shape of the positive electrode is not particularly limited and may beappropriately selected depending on the intended purpose. Examples ofthe shape include plate shapes and spherical shapes.

—Positive Electrode Material—

The positive electrode material is not particularly limited and may beappropriately selected depending on the intended purpose. For example,the positive electrode material includes at least a positive-electrodeactive material, and may further include a conduction auxiliary agent, abinder, a thickening agent, etc., according to the necessity.

——Positive-Electrode Active Material——

As the positive-electrode active material, porous carbon havingcommunicating pores “mesopores” of a three-dimensional network structureis used. The “positive-electrode active material having communicatingmesopores of a three-dimensional network structure” is a capacitor, inwhich an electric double layer is formed by a pair of positive andnegative electrolyte ions that are present over both sides of a facewhere mesopores (void areas) and a carbon material area are in contactwith each other. Therefore, it can be understood that movements ofelectrolyte ions present as a pair are faster than the movements ofelectrolyte ions generated after a sequential chemical reaction with anelectrode active material, and an ability of supplying electricitydepends on, not only a size of a volume of the void areas, but also asize of a surface area of mesopores, which allows a pair of positive andnegative electrolyte ions to be present.

Considering crystallinity of the porous carbon, the time constant (slowresponse during charge and discharge) of the capacitor depends on, notonly capacitance of a non-aqueous electrolyte, but also a resistancevalue of the carbon material area, with which the electrolyte forms anohmic contact. Since both electrolyte ions perform chemical reactions,in which binding and separation with the electrode active materials arerepeated, moreover, there is a possibility that the porous carbon isdeteriorated. The crystallinity of the porous carbon is preferablyappropriately determined so as to have strength resistant to theabove-described deterioration.

Note that, it is not necessary to have a crystalline structure in theentire area of the carbon material. An amorphous part may be present atpart of the porous carbon, or the entire porous carbon may be amorphous.

In the porous carbon, presence of mesopores is essential but presence ofmicropores is not essential. Accordingly, micropores may be present ormay not be present, but at the time of carbonization, an organicmaterial serving as a starting material of the carbon material typicallyreleases a volatile material to carbonize. Accordingly, micropores aretypically left as release marks, and therefore it is difficult to obtaina carbon material, which does not have micropores at all. On the otherhand, mesopores are typically intentionally formed. As it has been knownin the art, for example, it is often a case where a mark-formingmaterial of an acid (alkali)-soluble metal, metal oxide, metal salts, ormetal-containing organic material, and a carbon material or an organicmaterial that is a raw material of the carbon material are shapedtogether, then the mark-forming material is dissolved with acid(alkali), and the marks left become mesopores.

In the present specification, pores having diameters of less than 2 nmare referred to as micropores, and pores having diameters of 2 nm orgreater but 50 nm or less are referred to as mesopores. Since a size ofthe electrolyte ion is 0.5 nm or greater but 2 nm or less, it cannot besaid that the micropores significantly contribute to movements of theions. Accordingly, the presence of mesopores is important for smoothmovements of the ions. For comparison, a size of pores in activatedcarbon, which is also a carbonaceous material, is known to be about 1 nmon average. In case of the activated carbon, it is regarded as one ofadsorptions all of which generate heat (reduction in enthalpy) withoutexceptions.

The mesopores in the above-mentioned size preferably constitute athree-dimensional network structure. When the pores constitute athree-dimensional network structure, ions move smoothly.

A BET specific surface area of the porous carbon is preferably 50 m²/gor greater. When the BET specific surface area is 50 m²/g or greater, asufficient amount of pores is formed and insertion of ions issufficiently performed, hence a capacity of a resultantelectricity-storage element can be made high.

On the other hand, a BET specific surface area of the porous carbon ispreferably 2,000 m²/g or less. When the BET specific surface area is2,000 m²/g or less, mesopores are sufficiently formed, insertion of ionsis not inhibited, and therefore a high capacity can be obtained.

The BET specific surface area is more preferably 800 m²/g or greater but1,800 m²/g or less.

For example, the BET specific surface area can be measured by gasadsorption, etc.

The mesopores are open pores and preferably have a structure where poreareas communicate. With such a structure, ions are smoothly moved.

A pore volume of the porous carbon measured by the BJH method ispreferably 0.2 mL/g or greater but 2.3 mL/g or less, and more preferably0.2 mL/g or greater but 1.7 mL/g or less. When the pore volume is 0.2mL/g or greater, mesopores rarely become independent pores in whichcommunicating areas of the mesopores are blocked, and a large dischargecapacity can be obtained without inhibiting movements of ions. When thepore volume is 2.3 mL/g or less, on the other hand, reduction in densityas an electrode caused because the carbon is bulky can be prevented andhence reduction in a capacity per unit volume can be prevented.Moreover, deterioration of cycle properties can be prevented where thecycle properties are deteriorated because carbonaceous wallsconstituting the pores become thin and shapes of the carbonaceous wallcannot be maintained after insertion and release of ions are repeated.

For example, the pore volume can be measured by the BJH (Barrett,Joyner, Hallender) method according to gas adsorption.

——Binder and Thickening Agent——

The binder and the thickening agent are not particularly limited and maybe appropriately selected depending on the intended purpose, as long asthe binder and the thickening agent are materials stable to a solventused during production of an electrode or an electrolyte, or potentialapplied. Examples of the binder and the thickening agent include:fluorine-based binders, such as polyvinylidene fluoride (PVDF) andpolytetrafluoroethylene (PTFE); ethylene-propylene-butadiene rubber(EPBR); styrene-butadiene rubber (SBR); isoprene rubber; acrylate-basedlatex; carboxymethyl cellulose (CMC); methyl cellulose; hydroxylmethylcellulose; ethyl cellulose; polyacrylic acid; polyvinyl alcohol;aliginic acid; oxidized starch; starch phosphate; and casein. These maybe used alone or in combination. Among them, fluorine-based binders,such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene(PTFE), acrylate-based latex, and carboxymethyl cellulose (CMC) arepreferable.

——Conduction Auxiliary Agent——

Examples of the conduction auxiliary agent include: metal materials,such as copper and aluminium; and carbonaceous materials, such as carbonblack, acetylene black, and carbon nanotubes. These may be used alone orin combination.

—Positive-Electrode Collector—

A material, shape, size, and structure of the positive-electrodecollector are not particularly limited and may be appropriately selecteddepending on the intended purpose.

A material of the positive-electrode collector is not particularlylimited and may be appropriately selected depending on the intendedpurpose, as long as the material is formed of a conductive material andis stable against applied potential. Examples of the material of thepositive-electrode collector include stainless steel, nickel, aluminium,titanium, and tantalum. Among them, stainless steel and aluminium areparticularly preferable.

A shape of the positive-electrode collector is not particularly limitedand may be appropriately selected depending on the intended purpose.

A size of the positive-electrode collector is not particularly limitedand may be appropriately selected depending on the intended purpose, aslong as the size is a size usable for a non-aqueous electrolyteelectricity-storage element.

<Production Method of Positive Electrode>

As the positive electrode, a film of a positive electrode including apositive-electrode active material can be produced by adding the binder,the thickening agent, the conductive auxiliary agent, a solvent, etc.according to the necessity, to the positive-electrode active material toform a positive electrode material in the form of slurry, applying thepositive electrode material onto the positive electrode collector, anddrying the applied positive electrode material. The solvent is notparticularly limited and may be appropriately selected depending on theintended purpose. Examples of the solvent include aqueous solvents andorganic solvents. Examples of the aqueous solvents include water andalcohol. Examples of the organic solvents include N-methyl-2-pyrrolidone(NMP) and toluene.

Note that, the positive electrode-active material may be subjected toroll molding as it is to form a sheet electrode, or to compressionmolding to form a pellet electrode.

<Negative Electrode>

The negative electrode is not particularly limited and may beappropriately selected depending on the intended purpose, as long as thenegative electrode includes a negative-electrode active material.Examples of the negative electrode include a negative electrode in whicha negative-electrode material including a negative-electrode activematerial is disposed on a negative-electrode collector.

A shape of the negative electrode is not particularly limited and may beappropriately selected depending on the intended purpose. Examples ofthe shape include a plate shape.

—Negative-Electrode Material—

The negative-electrode material includes at least a negative-electrodeactive material, and may further include a conduction auxiliary agent, abinder, a thickening agent, etc., according to the necessity.

——Negative-Electrode Active Material——

The negative-electrode active material is not particularly limited aslong as the negative-electrode active material is capable of insertingand releasing lithium ions at least in a non-aqueous solvent system.Specific examples of the negative-electrode active material includecarbonaceous materials, metal oxides capable of inserting and releasinglithium, such as antimony-doped tin oxide and silicon monoxide, metalsof metal alloys capable of forming an alloy with lithium, such asaluminium, thin, silicon, and zinc, composite alloy compounds eachincluding a metal capable of forming an alloy with lithium, an alloyincluding the metal and lithium, and metal lithium nitride such ascobalt lithium nitride. These may be used alone or in combination. Amongthem, a carbonaceous material is particularly preferable in view ofsafety and a cost.

Examples of the carbonaceous material include: black lead (graphite),such as coke, artificial black lead, and natural black lead; and thermaldecomposition products of organic materials under various thermaldecomposition conditions. Among them, artificial black lead and naturalblack lead are particularly preferable.

——Binder and Thickening Agent——

The binder and the thickening agent are not particularly limited and maybe appropriately selected depending on the intended purpose, as long asthe binder and the thickening agent are materials stable to a solventused during production of an electrode or an electrolyte, or potentialapplied. Examples of the binder and the thickening agent include:fluorine-based binders, such as polyvinylidene fluoride (PVDF) andpolytetrafluoroethylene (PTFE); ethylene-propylene-butadiene rubber(EPBR); styrene-butadiene rubber (SBR); isoprene rubber; acrylate-basedlatex; carboxymethyl cellulose (CMC); methyl cellulose; hydroxylmethylcellulose; ethyl cellulose; polyacrylic acid; polyvinyl alcohol;aliginic acid; oxidized starch; starch phosphate; and casein. These maybe used alone or in combination. Among them, fluorine-based binders,such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene(PTFE), styrene-butadiene rubber (SBR), and carboxymethyl cellulose(CMC) are preferable.

——Conduction Auxiliary Agent——

Examples of the conduction auxiliary agent include: metal materials,such as copper and aluminium; and carbonaceous materials, such as carbonblack, acetylene black, and carbon nanotubes. These may be used alone orin combination.

—Negative-Electrode Collector—

A material, shape, size and structure of the negative-electrodecollector are not particularly limited and may be appropriately selecteddepending on the intended purpose.

A material of the negative-electrode collector is not particularlylimited and may be appropriately selected depending on the intendedpurpose, as long as the material is formed of a conductive material andis stable against applied potential. Examples of the material includestainless steel, nickel, aluminium, and copper. Among them, stainlesssteel, copper, and aluminium are particularly preferable.

A shape of the collector is not particularly limited and may beappropriately selected depending on the intended purpose.

A size of the collector is not particularly limited and may beappropriately selected depending on the intended purpose, as long as thesize is a size usable for a non-aqueous electrolyte electricity-storageelement.

<Production Method of Negative Electrode>

The negative electrode can be produced by adding the binder, thethickening agent, the conduction auxiliary agent, a solvent, etc.according to the necessity, to the negative-electrode active material toform a negative electrode material in the form of slurry, applying thenegative electrode material onto the negative electrode collector, anddrying the applied negative electrode material. As the solvent, any ofthe solvents listed as examples of the solvent for use in the productionmethod of the positive electrode can be used.

Moreover, the negative-electrode active material, to which the binder,the thickening agent, the conduction auxiliary agent, etc., are added,may be subjected to roll molding as it is to form a sheet electrode, orto compression molding to form a pellet electrode, or a method, such asvapor deposition, sputtering, and plating, to form a thin film of thenegative-electrode active material on the negative electrode collector.

<Non-Aqueous Electrolyte>

The non-aqueous electrolyte is an electrolyte formed by dissolving anelectrolyte salt in a non-aqueous solvent.

—Non-Aqueous Solvent—

The non-aqueous solvent is not particularly limited and may beappropriately selected depending on the intended purpose. Thenon-aqueous solvent is suitably an aprotic organic solvent.

As the aprotic organic solvent, a carbonate-based organic solvent, suchas chain carbonate and cyclic carbonate, is used. The aprotic organicsolvent is preferably a solvent of low viscosity. Among the above-listedsolvents, chain carbonate is preferable because the chain carbonate hashigh solubility to an electrolyte salt. Among then, chain carbonate ispreferable because the chain carbonate has a high dissolving poweragainst an electrolyte salt.

Examples of the chain carbonate include dimethyl carbonate (DMC),diethyl carbonate (DEC), and methyl ethyl carbonate (EMC). Among them,dimethyl carbonate (DMC) is preferable.

An amount of the DMC is not particularly limited and may beappropriately selected depending on the intended purpose, but the amountof the DMC is preferably 70% by mass or greater relative to thenon-aqueous solvent. When the amount of the DMC is 70% by mass orgreater, even in a case where the rest of the solvent is the cyclicmaterial having a high dielectric constant (e.g., cyclic carbonate andcyclic ester), an amount of a cyclic material having a high dielectricconstant is not large, and therefore a viscosity does not become higheven when a non-aqueous electrolyte of high concentration of 3 mol/L orgreater is produced, hence problems, such as penetration of anon-aqueous electrolyte into an electrode and diffusion of ions, do notoccur.

Examples of the cyclic carbonate include propylene carbonate (PC),ethylene carbonate (EC), butylene carbonate (BC), vinylene carbonate(VC), and fluoroethylene carbonate (FEC).

When ethylene carbonate (EC) as the cyclic carbonate and dimethylcarbonate (DMC) as the chain carbonate are used in combination as amixed solvent, a blending ratio between ethylene carbonate (EC) anddimethyl carbonate (DMC) is not particularly limited and may beappropriately selected depending on the intended purpose. A mass ratio(EC:DMC) is preferably from 3:10 through 1:99 and more preferably from3:10 through 1:20.

As the non-aqueous solvent, ester-based organic solvents, such as cyclicester and chain ester, and ether-based organic solvents, such as cyclicether and chain ether, may be used according to the necessity.

Examples of the cyclic ester include γ-butyrolactone (γ-BL),2-methyl-γ-butyrolactone, acetyl-γ-butyrolactone, and γ-valerolactone.

Examples of the chain ester include alkyl propionate, dialkyl malonate,alkyl acetate (methyl acetate (MA), ethyl acetate, etc.), and alkylformate (methyl formate (ME), ethyl formate, etc.).

Examples of the cyclic ether include tetrahydrofuran,alkyltetrahydrofuran, alkoxy tetrahydrofuran, dialkoxy tetrahydrofuran,1,3-dioxolan, alkyl-1,3-dioxolan, and 1,4-dioxolan.

Examples of the chain ether include 1,2-dimethoxyethane (DME), diethylether, ethylene glycol dialkyl ether, diethylene glycol dialkyl ether,triethylene glycol dialkyl ether, and tetraethylene glycol dialkylether.

—Electrolyte Salt—

A lithium salt is used as the electrolyte salt. The lithium salt is notparticularly limited as long as the lithium salt is dissolved in anon-aqueous solvent to exhibits high ion conductivity. Examples of thelithium salt include lithium hexafluorophosphate (LiPF₆), lithiumperchlorate (LiClO₄), lithium chloride (LiCl), lithium fluoroborate(LiBF₄), lithium hexafluoroarsenate (LiAsF₆), lithiumtrifluoromethanesulfonate (LiCF₃SO₃), lithium bistrifluoromethylsulfonylimide (LiN(CF₃SO₂)₂), and lithium bisperfluoroethylsulfonyl imide(LiN(C₂F₅SO₂)₂). These may be used alone or in combination. Among them,LiPF₆ is particularly preferable because of a large amount of anionsaccumulated in a carbon electrode.

A concentration of the electrolyte salt is not particularly limited andmay be appropriately selected depending on the intended purpose. Theconcentration of the electrolyte salt in the non-aqueous solvent ispreferably 0.5 mol/L or greater but 6 mol/L or less, and more preferably2 mol/L or greater but 4 mol/L or less in view of both a capacity andoutput of the electricity-storage element.

<Separator>

The separator is disposed between the positive electrode and thenegative electrode for preventing a short circuit between the positiveelectrode and the negative electrode.

A material, shape, size, and structure of the separator is notparticularly limited and may be appropriately selected depending on theintended purpose.

Examples of a material of the separator include: paper such as Kraftpaper, vinylon blended paper, and synthetic pulp blended paper;cellophane; polyethylene graft membranes; polyolefin nonwoven fabric,such as polypropylene melt-flow nonwoven fabric; glass fiber nonwovenfabric; and micropore membranes. These may be used alone or incombination. Among them, a material having a porosity of 50% or greateris preferable in view of retention of an electrolyte.

As the shape of the separator, a nonwoven fabric is more preferable thana thin film-type having fine pores (micropores) because the nonwovenfabric has a high porosity.

A thickness of the separator is preferably 20 μm or greater in view ofprevention of a short circuit and retention of an electrolyte.

A size of the separator is not particularly limited and may beappropriately selected depending on the intended purpose, as long as thesize is a size usable for the non-aqueous electrolyteelectricity-storage element.

A structure of the separator may be a single-layer structure or alaminate structure.

<Production Method of Non-Aqueous Electrolyte Electricity-StorageElement>

A non-aqueous electrolyte electricity-storage element of the presentdisclosure can be produced by assembling the positive electrode, thenegative electrode, the non-aqueous electrolyte, and optionally aseparator into an appropriate shape. Moreover, other constitutionalmembers, such as an outer tin, can be used according to the necessity. Amethod for assembling the non-aqueous electrolyte electricity-storageelement is not particularly limited and may be appropriately selectedfrom methods typically used.

A shape of the non-aqueous electrolyte electricity-storage element ofthe present disclosure is not particularly limited and may beappropriately selected from various shapes typically used depending onthe intended use. Examples of the shape include a cylinder-type wheresheet electrodes and a separator are spirally disposed, a cylinder-typehaving an inside-out structure where pellet electrodes and a separatorare combined, and a coin-type where pellet electrodes and a separatorare laminated.

Here, FIG. 1 is a schematic view illustrating one example of anon-aqueous electrolyte electricity-storage element of the presentdisclosure. The non-aqueous electrolyte electricity-storage element 10illustrated in FIG. 1 includes, inside an outer tin 4, a positiveelectrode 1, a negative electrode 2, and a separator 3 including thenon-aqueous electrolyte. To the non-aqueous electrolyteelectricity-storage element, a negative-electrode lead-out line 5 and apositive-electrode lead-out line 6 are disposed.

<Use>

Use of the non-aqueous electrolyte electricity-storage element of thepresent disclosure is not particularly limited and the non-aqueouselectrolyte electricity-storage element can be used for various types ofuse. Examples of the use of the non-aqueous electrolyteelectricity-storage element include power sources or back-up powersources for laptop computers, stylus-operated computers, mobilecomputers, electronic book players, mobile phones, mobile facsimiles,mobile photocopiers, mobile printers, headphone stereos, video movieplayers, liquid crystal televisions, handy cleaners, portable CDplayers, minidisk players, transceivers, electronic organizers,calculators, memory cards, mobile tape recorders, radios, motors,lighting equipment, toys, game equipment, clocks, strobes, and cameras.

EXAMPLES

Examples of the present disclosure will be described hereinafter, butthe present disclosure should not be construed as being limited to theseExamples.

Example 1 <Production of Positive Electrode>

Carbon A (amorphous CNOVEL, available from Toyo Tanso Co., Ltd.) servingas a positive-electrode active material, acetylene black (Denka Blackpowder, available from Denka Company Limited) serving as a conductionauxiliary agent, acrylate-based latex (TRD202A, available from JSRCorporation) serving as a binder, and carboxymethyl cellulose (DAICEL1270, available from Daicel Corporation) serving as a thickening agentwere mixed in a manner that a mass ratio of the mixture based on each ofthe solid contents was to be 100:7.5:3.0:9.5. Water was added to theresultant mixture to adjust the viscosity of the mixture to anappropriate degree, to thereby obtain a slurry. Subsequently, theobtained slurry was applied onto one side of an aluminium foil having athickness of 20 μm using a doctor blade, and the applied slurry wasdried followed by cutting out into a circle having a diameter of 16 mmto thereby obtain a positive electrode.

An average applied amount of the positive-electrode active material inthe positive electrode film after drying was 2.3 mg/cm².

<Production of Electricity-Storage Element>

An electricity-storage element was produced using the Positive ElectrodeAbove, 2 Sheets of Glass Filter Paper (GA100, available from ADVANTEC)each of which was cut out into a circle having a diameter of 16 mm as aseparator, a lithium metal foil having a diameter of 16 mm as a negativeelectrode, and an EC/DMC/FEC (mass ratio: 2:96:2) mixed solution(available from KISHIDA CHEMICAL Co., Ltd.) including 2 mol/L of a LiPF₆electrolyte as an electrolyte. Specifically, after vacuum drying thepositive electrode and the separator for 4 hours at 150° C., a 2032 coincell was assembled in a dry argon glove box.

<Evaluations of Electricity-Storage Element>

A charge-discharge test was performed by means of an automatic cellevaluation device (1024B-7V0.1A-4, available from Electro Field Co.,Ltd.) with maintaining the electricity-storage element in a thermostaticchamber of 25° C.

A reference current value was set to 0.5 mA, and charge was performedwith cut-off voltage of 4.5 V and discharge was performed with cut-offvoltage of 1.5 V, and an interval of 5 minutes was provided betweencharge and discharge, and between the discharge and the followingcharge.

A combination of the charge and the discharge under the conditions abovewas determined as 1 cycle, and the charge-discharge test was performedup to 50 cycles. Moreover, a separate electricity-storage elementproduced in the same manner as above was prepared, and a measurement wasperformed in the same manner as above under the same measuringconditions. When a discharge capacity of this electricity-storageelement at 50th cycle was determined as 100%, the cycle was repeateduntil a discharge capacity maintaining rate was to be 80% or less.However, the upper limit of the cycle measuring times was set to 1,000cycles.

<Measurement of Changing Rate of Cross-Sectional Thickness of PositiveElectrode Film>

When a changing rate of a cross-sectional thickness of the positiveelectrode film was measured, a sample to which the charge-discharge testhad been performed up to 50 cycles was used to determine a changing rateof the cross-sectional thickness of the positive electrode film.Specifically, at first, a cross-sectional film thickness of the positiveelectrode film before the charge-discharge cycle test was measured bymeans of a digital gage (DG-205, available from OZAKI MFG. CO., LTD.).

Next, the positive electrode film was taken out from theelectricity-storage element after performing the cycle test, and athickness of the positive electrode film after the cycle test wasmeasured in the same manner as the measurement before the cycle test.Finally, a changing rate of the cross-sectional thickness defined byFormula (1) below was calculated. Note that, the cross-sectional filmthickness of the positive electrode film was an average value of valuesmeasured at randomly selected 3 points of the positive electrode filmusing the digital gage.

$\begin{matrix}{\begin{matrix}{{Changing}\mspace{14mu} {rate}\mspace{14mu} {of}} \\{{cross}\text{-}{sectional}\mspace{14mu} {thickness}\mspace{11mu} (\%)}\end{matrix} = {\frac{\begin{matrix}{{{Film}\mspace{14mu} {thickness}\mspace{14mu} {after}\mspace{14mu} {charge}\text{-}{discharge}} -} \\{{Film}\mspace{14mu} {thickness}\mspace{14mu} {before}\mspace{14mu} {charge}\text{-}{discharge}}\end{matrix}}{{Film}\mspace{14mu} {thickness}\mspace{14mu} {before}\mspace{14mu} {charge}\text{-}{discharge}} \times 100}} & {{Formula}\mspace{14mu} (1)}\end{matrix}$

Note that, the methods and conditions for measuring the changing rate ofthe cross-sectional thickness and the cycle properties were the same inthe evaluations of the changing rate of the cross-sectional thicknessand the cycle properties in the following series of Examples andComparative Examples.

The physical properties values of the positive-electrode activematerial, and as the charge-discharge measurement results, the dischargecapacity of the 50th cycle with the reference current value, thechanging rate of the thickness, and the number of cycles at the pointwhen the discharge capacity retention rate is 80% or less (cycle servicelife), when the discharge capacity of the 50th cycle is determined as100%, are presented in Table 1.

Note that, the BET specific surface area was calculated according to theBET method from the result of adsorption isotherm measured byTriStar3020 (available from Shimadzu Corporation). The pore volume wascalculated according to the BJH method. The discharge capacity is a massconversion value per a unit mass of the positive-electrode activematerial.

Comparative Example 1 <Production of Positive Electrode>

Black lead powder (KS-6, available from TIMCAL) serving as apositive-electrode active material, acetylene black (Denka Black powder,available from Denka Company Limited) serving as a conduction auxiliaryagent, acrylate-based latex (TRD202A, available from JSR Corporation)serving as a binder, and carboxymethyl cellulose (DAICEL 2200, availablefrom Daicel Corporation) serving as a thickening agent were mixed in amanner that a mass ratio of the mixture based on each of the solidcontents was to be 100:7.5:3.0:3.8. Water was added to the resultantmixture to adjust the viscosity of the mixture to an appropriate degree,to thereby obtain a slurry. Subsequently, the obtained slurry wasapplied onto one side of an aluminium foil having a thickness of 20 μmusing a doctor blade, and the applied slurry was dried followed bycutting out into a circle having a diameter of 16 mm to thereby obtain apositive electrode.

An average applied amount of the positive-electrode active material inthe positive electrode film after drying was 5 mg/cm².

<Production and Evaluations of Electricity-Storage Element>

An electricity-storage element was produced in the same manner as inExample 1, except that the positive electrode above was used.

A charge-discharge test was performed on the obtainedelectricity-storage element in the same manner as in Example 1, exceptthat, as the measuring conditions, a reference current value was set to1.0 mA, charge was performed with cut-off voltage of 5.2 V, dischargewas performed with cut-off voltage of 3.0 V, and an interval of 5minutes was provided between charge and discharge, and between thedischarge and the following charge.

Values of physical properties of the positive-electrode active materialand the evaluation results are presented in Table 1.

Comparative Example 2

A positive electrode and an electricity-storage element were produced inthe same manner as in Comparative Example 1, except that as apositive-electrode active material, activated carbon (BELLFINE AP,available from ATELECTRODE CO., LTD.) was used. Evaluations wereperformed in the same manner as in Example 1. Values of physicalproperties of the positive-electrode active material and the evaluationresults are presented in Table 1.

Charge-discharge curves of cycles of Example 1 are presented in FIG. 2,those of Comparative Example 1 are presented in FIG. 3, and those ofComparative Example 2 are presented in FIG. 4. It was found from theresults of Table 1 and FIGS. 2 to 4 that Example 1 of the presentdisclosure, whereas the positive-electrode active material, the carbonthat had pores of a three-dimensional network structure was used and thechanging rate of the cross-sectional thickness of the positive electrodefilm was less than 45%, had the large discharge capacity at the 50thcycle, and the changing rate of the cross-sectional thickness of thepositive electrode film was small and hence had excellent cycleproperties, compared to Comparative Example 1 where the black lead thatdid not have pores of a three-dimensional network structure was used. Itwas assumed that the cycle service life was excellent in Example 1because the changing rate of the cross-sectional thickness of thepositive electrode film was small.

Moreover, in Comparative Example 2 where the activated carbon that didnot have pores of a three-dimensional network structure was used, thechanging rate of the cross-sectional thickness of the positive electrodefilm and the cycle properties were excellent, but the discharge capacitywas extremely small.

Example 2

A positive electrode and an electricity-storage element were produced inthe same manner as in Example 1, except that as a positive-electrodeactive material, Carbon B (amorphous CNOVEL, available from Toyo TansoCo., Ltd.) was used. Evaluations were performed in the same manner as inExample 1. Values of physical properties of the positive-electrodeactive material and the evaluation results are presented in Table 1.

Example 3

A positive electrode and an electricity-storage element were produced inthe same manner as in Example 1, except that as a positive-electrodeactive material, Carbon C (amorphous CNOVEL, available from Toyo TansoCo., Ltd.) was used. Evaluations were performed in the same manner as inExample 1. Values of physical properties of the positive-electrodeactive material and the evaluation results are presented in Table 1.

Example 4

A positive electrode and an electricity-storage element were produced inthe same manner as in Example 1, except that as a positive-electrodeactive material, Carbon D (amorphous CNOVEL, available from Toyo TansoCo., Ltd.) was used. Evaluations were performed in the same manner as inExample 1. Values of physical properties of the positive-electrodeactive material and the evaluation results are presented in Table 1.

Example 5

A positive electrode and an electricity-storage element were produced inthe same manner as in Example 1, except that as a positive-electrodeactive material, Carbon E (amorphous CNOVEL, available from Toyo TansoCo., Ltd.) was used. Evaluations were performed in the same manner as inExample 1. Values of physical properties of the positive-electrodeactive material and the evaluation results are presented in Table 1.

Example 6

A charge-discharge test was performed on the electricity-storage elementof Example 1 in the same manner as in Example 1, except that a referencecurrent value was set to 0.5 mA, charge was performed with cut-offvoltage of 4.7 V, discharge was performed with cut-off voltage of 1.5 V,and an interval of 5 minutes was provided between charge and discharge,and between the discharge and the following charge. Values of physicalproperties of the positive-electrode active material and the evaluationresults are presented in Table 1.

Example 7

A charge-discharge test was performed on the electricity-storage elementof Example 1 in the same manner as in Example 1, except that a referencecurrent value was set to 0.5 mA, charge was performed with cut-offvoltage of 4.8 V, discharge was performed with cut-off voltage of 1.5 V,and an interval of 5 minutes was provided between charge and discharge,and between the discharge and the following charge. Values of physicalproperties of the positive-electrode active material and the evaluationresults are presented in Table 1.

Example 8 <Production of Positive Electrode>

Carbon F (crystalline CNOVEL, available from Toyo Tanso CO., Ltd.)serving as a positive-electrode active material, acetylene black (DenkaBlack powder, available from Denka Company Limited) serving as aconduction auxiliary agent, acrylate-based latex (TRD202A, availablefrom JSR Corporation) serving as a binder, and carboxymethyl cellulose(DAICEL 1270, available from Daicel Corporation) serving as a thickeningagent were mixed in a manner that a mass ratio of the mixture based oneach of the solid contents was to be 100:7.5:3.0:10. Water was added tothe resultant mixture to adjust the viscosity of the mixture to anappropriate degree, to thereby obtain a slurry. Subsequently, theobtained slurry was applied onto one side of an aluminium foil having athickness of 20 μm using a doctor blade, and the applied slurry wasdried followed by cutting out into a circle having a diameter of 16 mmto thereby obtain a positive electrode.

An average applied amount of the positive-electrode active material inthe positive electrode film after drying was 2.0 mg/cm².

<Production and Evaluations of Electricity-Storage Element>

An electricity-storage element was produced in the same manner as inExample 1, except that the positive electrode above was used.

A charge-discharge test was performed on the obtainedelectricity-storage element in the same manner as in Example 1, exceptthat, as the measuring conditions, a reference current value was set to1.0 mA, charge was performed with cut-off voltage of 5.2 V, dischargewas performed with cut-off voltage of 2.0 V, and an interval of 5minutes was provided between charge and discharge, and between thedischarge and the following charge. Values of physical properties of thepositive-electrode active material and the evaluation results arepresented in Table 1.

Example 9

A positive electrode and an electricity-storage element were produced inthe same manner as in Example 8, except that as a positive-electrodeactive material, Carbon G (crystalline CNOVEL, available from Toyo TansoCo., Ltd.) was used. Evaluations were performed in the same manner as inExample 1, except that measuring conditions were the same as in Example8. Values of physical properties of the positive-electrode activematerial and the evaluation results are presented in Table 1.

Example 10

A positive electrode and an electricity-storage element were produced inthe same manner as in Example 8, except that as a positive-electrodeactive material, Carbon H (crystalline CNOVEL, available from Toyo TansoCo., Ltd.) was used. Evaluations were performed in the same manner as inExample 1, except that measuring conditions were the same as in Example8. Values of physical properties of the positive-electrode activematerial and the evaluation results are presented in Table 1.

Example 11

A charge-discharge test was performed on the electricity-storage elementof Example 8 in the same manner as in Example 1, except that a referencecurrent value was set to 1.0 mA, charge was performed with cut-offvoltage of 5.3 V, discharge was performed with cut-off voltage of 2.0 V,and an interval of 5 minutes was provided between charge and discharge,and between the discharge and the following charge. Values of physicalproperties of the positive-electrode active material and the evaluationresults are presented in Table 1.

Example 12 <Production of Positive Electrode>

Carbon I (non-graphitizable CNOVEL, available from Toyo Tanso Co., Ltd.)serving as a positive-electrode active material, acetylene black (DenkaBlack powder, available from Denka Company Limited) serving as aconduction auxiliary agent, acrylate-based latex (TRD202A, availablefrom JSR Corporation) serving as a binder, and carboxymethyl cellulose(DAICEL 1270, available from Daicel Corporation) serving as a thickeningagent were mixed in a manner that a mass ratio of the mixture based oneach of the solid contents was to be 100:7.5:3.0:10. Water was added tothe resultant mixture to adjust the viscosity of the mixture to anappropriate degree, to thereby obtain a slurry. Subsequently, theobtained slurry was applied onto one side of an aluminium foil having athickness of 20 μm using a doctor blade, and the applied slurry wasdried followed by cutting out into a circle having a diameter of 16 mmto thereby obtain a positive electrode.

An average applied amount of the positive-electrode active material inthe positive electrode film after drying was 1.7 mg/cm².

<Production and Evaluations of Electricity-Storage Element>

An electricity-storage element was produced in the same manner as inExample 1, except that the positive electrode above was used.

An evaluation was performed on the obtained electricity-storage elementin the same manner as in Example 1, except that a reference currentvalue was set to 1.0 mA, charge was performed with cut-off voltage of5.2 V, discharge was performed with cut-off voltage of 2.0 V, and aninterval of 5 minutes was provided between charge and discharge, andbetween the discharge and the following charge. Values of physicalproperties of the positive-electrode active material and the evaluationresults are presented in Table 1.

Example 13

A positive electrode and an electricity-storage element were produced inthe same manner as in Example 12, except that as a positive-electrodeactive material, Carbon J (non-graphitizable CNOVEL, available from ToyoTanso Co., Ltd.) was used. Evaluations were performed in the same manneras in Example 1, except that measuring conditions were the same as inExample 12. Values of physical properties of the positive-electrodeactive material and the evaluation results are presented in Table 1.

Example 14

A positive electrode and an electricity-storage element were produced inthe same manner as in Example 12, except that as a positive-electrodeactive material, Carbon K (non-graphitizable CNOVEL, available from ToyoTanso Co., Ltd.) was used. Evaluations were performed in the same manneras in Example 1, except that measuring conditions were the same as inExample 12. Values of physical properties of the positive-electrodeactive material and the evaluation results are presented in Table 1.

Example 15

A positive electrode and an electricity-storage element were produced inthe same manner as in Example 12, except that as a positive-electrodeactive material, Carbon L (non-graphitizable CNOVEL, available from ToyoTanso Co., Ltd.) was used. Evaluations were performed in the same manneras in Example 1, except that measuring conditions were the same as inExample 12. Values of physical properties of the positive-electrodeactive material and the evaluation results are presented in Table 1.

Example 16

A positive electrode and an electricity-storage element were produced inthe same manner as in Example 12, except that as a positive-electrodeactive material, Carbon M (non-graphitizable CNOVEL, available from ToyoTanso Co., Ltd.) was used. Evaluations were performed in the same manneras in Example 1, except that measuring conditions were the same as inExample 12. Values of physical properties of the positive-electrodeactive material and the evaluation results are presented in Table 1.

Example 17

A positive electrode and an electricity-storage element were produced inthe same manner as in Example 12, except that as a positive-electrodeactive material, Carbon N (non-graphitizable CNOVEL, available from ToyoTanso Co., Ltd.) was used. Evaluations were performed in the same manneras in Example 1, except that measuring conditions were the same as inExample 12. Values of physical properties of the positive-electrodeactive material and the evaluation results are presented in Table 1.

Example 18

A charge-discharge test was performed on the electricity-storage elementof Example 16 in the same manner as in Example 1, except that areference current value was set to 1.0 mA, charge was performed withcut-off voltage of 4.7 V, discharge was performed with cut-off voltageof 2.0 V, and an interval of 5 minutes was provided between charge anddischarge, and between the discharge and the following charge. Values ofphysical properties of the positive-electrode active material and theevaluation results are presented in Table 1.

Example 19

A charge-discharge test was performed on the electricity-storage elementof Example 16 in the same manner as in Example 1, except that areference current value was set to 1.0 mA, charge was performed withcut-off voltage of 4.8 V, discharge was performed with cut-off voltageof 2.0 V, and an interval of 5 minutes was provided between charge anddischarge, and between the discharge and the following charge. Values ofphysical properties of the positive-electrode active material and theevaluation results are presented in Table 1.

Example 20

A charge-discharge test was performed on the electricity-storage elementof Example 16 in the same manner as in Example 1, except that areference current value was set to 1.0 mA, charge was performed withcut-off voltage of 5.0 V, discharge was performed with cut-off voltageof 2.0 V, and an interval of 5 minutes was provided between charge anddischarge, and between the discharge and the following charge. Values ofphysical properties of the positive-electrode active material and theevaluation results are presented in Table 1.

Example 21

A charge-discharge test was performed on the electricity-storage elementof Example 16 in the same manner as in Example 1, except that areference current value was set to 1.0 mA, charge was performed withcut-off voltage of 5.1 V, discharge was performed with cut-off voltageof 2.0 V, and an interval of 5 minutes was provided between charge anddischarge, and between the discharge and the following charge. Values ofphysical properties of the positive-electrode active material and theevaluation results are presented in Table 1.

Comparative Example 3 <Production of Positive Electrode>

Mesoporous carbon (Carbon, mesoporous, available from Sigma-Aldrich Co.LLC.) serving as a positive-electrode active material, acetylene black(Denka Black powder, available from Denka Company Limited) serving as aconduction auxiliary agent, acrylate-based latex (TRD202A, availablefrom JSR Corporation) serving as a binder, and carboxymethyl cellulose(DAICEL 2200, available from Daicel Corporation) serving as a thickeningagent were mixed in a manner that a mass ratio of the mixture based oneach of the solid contents was to be 100:7.5:5.8:17.8. Subsequently, theobtained slurry was applied onto one side of an aluminium foil having athickness of 20 μm using a doctor blade, and the applied slurry wasdried followed by cutting out into a circle having a diameter of 16 mmto thereby obtain a positive electrode.

An average applied amount of the positive-electrode active material inthe positive electrode film after drying was 2.4 mg/cm².

<Production and Evaluations of Electricity-Storage Element>

An electricity-storage element was produced in the same manner as inExample 1, except that the positive electrode above was used.

Evaluations were performed on the obtained electricity-storage elementin the same manner as in Example 1, except that, as the measuringconditions, a reference current value was set to 0.03 mA, and the othermeasuring conditions were same as in Comparative Example 1. Values ofphysical properties of the positive-electrode active material and theevaluation results are presented in Table 1.

Comparative Example 4 <Activation Treatment>

Graphitizable carbon (SC Grade, available from SEC CARBON, LIMITED) wasbaked at 900° C. in an argon atmosphere together with 2.5 parts by massof potassium hydroxide (KOH) relative to 1 part by mass of the usedgraphitizable carbon, to thereby obtain an activation-treated carbonmaterial.

A positive electrode and an electricity-storage element were produced inthe same manner as in Comparative Example 1, except that as apositive-electrode active material, the activation-treated carbonobtained above was used. Evaluations were performed in the same manneras in Example 1, except that measurement conditions were the same as inComparative Example 1. Values of physical properties of thepositive-electrode active material and the evaluation results arepresented in Table 1.

Comparative Example 5

Evaluations were performed on the electricity-storage element of Example1 in the same manner as in Example 1, except that a reference currentvalue was set to 0.5 mA, charge was performed with cut-off voltage of4.9 V, discharge was performed with cut-off voltage of 1.5 V, and aninterval of 5 minutes was provided between charge and discharge, andbetween the discharge and the following charge. Values of physicalproperties of the positive-electrode active material and the evaluationresults are presented in Table 1.

Comparative Example 6

Evaluations were performed on the electricity-storage element of Example8 in the same manner as in Example 1, except that a reference currentvalue was set to 1.0 mA, charge was performed with cut-off voltage of5.4 V, discharge was performed with cut-off voltage of 2.0 V, and aninterval of 5 minutes was provided between charge and discharge, andbetween the discharge and the following charge. Values of physicalproperties of the positive-electrode active material and the evaluationresults are presented in Table 1.

Comparative Example 7

Evaluations were performed on the electricity-storage element of Example16 in the same manner as in Example 1, except that a reference currentvalue was set to 1.0 mA, charge was performed with cut-off voltage of5.3 V, discharge was performed with cut-off voltage of 2.0 V, and aninterval of 5 minutes was provided between charge and discharge, andbetween the discharge and the following charge. Values of physicalproperties of the positive-electrode active material and the evaluationresults are presented in Table 1.

Comparative Example 8

Evaluations were performed on the electricity-storage element of Example16 in the same manner as in Example 1, except that a reference currentvalue was set to 1.0 mA, charge was performed with cut-off voltage of5.4 V, discharge was performed with cut-off voltage of 2.0 V, and aninterval of 5 minutes was provided between charge and discharge, andbetween the discharge and the following charge. Values of physicalproperties of the positive-electrode active material and the evaluationresults are presented in Table 1.

Next, the physical properties values of the positive-electrode activematerials of Examples 2 to 21 and Comparative Examples 3 to 8, and asthe charge-discharge measurement results of each of Examples 2 to 21 andComparative Examples 3 to 8, the discharge capacity of the 50th cyclewith the reference current value, the changing rate of the thickness,and the number of cycles at the point when the discharge capacityretention rate is 80% or less (cycle service life), when the dischargecapacity of the 50th cycle is determined as 100%, are presented in Table1.

Note that, the BET specific surface area was calculated according to theBET method from the result of adsorption isotherm measured byTriStar3020 (available from Shimadzu Corporation). The pore volume wascalculated according to the BJH method. The discharge capacity is a massconversion value per a unit mass of the positive-electrode activematerial.

TABLE 1 Presence BET Discharge Changing of 3D specific Pore capacity ofrate of Cycle network surface capacity 50^(th) cycle thickness servicelife Sample Carbon structure area (m²/g) (mL/g) (mAh/g) (%) (times) Ex.1 Carbon A: Present 1,730 2.27 106 13 1,000 amorphous Ex. 2 Carbon B:Present 1,991 2.30 130 19 892 amorphous Ex. 3 Carbon C: Present 1,4901.40 93 10 1,000 amorphous Ex. 4 Carbon D: Present 503 1.13 78 8 1,000amorphous Ex. 5 Carbon E: Present 2,014 2.37 47 22 173 amorphous Ex. 6Carbon A: Present 1,732 2.28 138 39 483 amorphous Ex. 7 Carbon A:Present 1,732 2.28 141 43 263 amorphous Ex. 8 Carbon F: Present 1,1301.51 96 39 523 crystalline Ex. 9 Carbon G: Present 800 1.03 89 28 811crystalline Ex. 10 Carbon H: Present 200 0.40 68 21 923 crystalline Ex.11 Carbon F: Present 1,130 1.51 112 43 256 crystalline Ex. 12 Carbon I:Present 48 0.19 48 4 1,000 nongraphitizable Ex. 13 Carbon J: Present 550.21 66 9 1,000 nongraphitizable Ex. 14 Carbon K: Present 90 0.24 73 17791 nongraphitizable Ex. 15 Carbon L: Present 562 0.75 89 38 683nongraphitizable Ex. 16 Carbon M: Present 860 0.98 95 43 563nongraphitizable Ex. 17 Carbon N: Present 1,100 1.45 98 38 628nongraphitizable Ex. 18 Carbon M: Present 860 0.98 47 10 1,000nongraphitizable Ex. 19 Carbon M: Present 860 0.98 51 14 1,000nongraphitizable Ex. 20 Carbon M: Present 860 0.98 67 25 793nongraphitizable Ex. 21 Carbon M: Present 860 0.98 82 44 548nongraphitizable Comp. Black lead Not 2.5 — 80 102 153 Ex. 1 presentComp. Activated carbon Not 1,732 1.20 45 7 1,000 Ex. 2 present Comp.Mesoporous Not 200 0.32 40 10 892 Ex. 3 carbon present Comp. Activation-Not 37 0.04 99 116 88 Ex. 4 treated carbon present Comp. Carbon A:Present 1,732 2.28 145 48 148 Ex. 5 amorphous Comp. Carbon F: Present1,130 1.51 132 49 35 Ex. 6 crystalline Comp. Carbon M: Present 860 0.98121 45 120 Ex. 7 nongraphitizable Comp. Carbon M: Present 860 0.98 14347 68 Ex. 8 nongraphitizable

It was found from the results of Table 1 that Examples 1 to 21 where, asthe positive-electrode active material, the carbon having the pores ofthe three-dimensional network structure was used and the changing rateof the cross-sectional thickness of the positive electrode film was lessthan 45%, all had a high discharge capacity of the 50th cycle comparedto Comparative Examples 2 and 3 where the activated carbon andmesoporous carbon were used, and all had excellent cycle service lifecompared to Comparative Examples 1 and 4 where the black lead and theactivation-treated carbon were used. Specifically, both properties ofthe high capacity and the long cycle service life were not able to beachieved at the same time when any of the carbons of ComparativeExamples 1 to 4 were used as the active material, but the bothproperties were achieved with the high values in Examples 1 to 21.

The discharge capacity of each of Examples 1 to 21 is preferably 50mAh/g or greater that is a superior difference to the discharge capacityof Comparative Example 2. As the discharge capacity increases, moreover,the changing rate of the cross-sectional thickness of the positiveelectrode film tends to be large, leading to degradation of the cycleservice life. In Example 7, particularly, the value of the cycle servicelife was significantly lower than the values in other Examples. Based onthe results above, the discharge capacity is preferably 140 mAh/g orlower.

As the values of the BET specific area and the pore capacity of each ofExamples 1 to 21 decrease, moreover, the value of the discharge capacitytends to decrease. In Example 12, particularly, the value of thedischarge capacity of the 50th cycle was slightly larger than the valueof Comparative Example 2, and was not a satisfactory level. Based on theresults above, the BET specific surface area is preferably 50 m²/g orgreater and the pore volume is preferably 0.2 mL/g or greater.

As the values of the BET specific surface area and the pore volumeincrease, the value of the discharge capacity tends to increase.However, the value of the discharge capacity decreases and the cycleservice life is shortens when the values of the BET specific area andthe pore volume are too large as in Example 5. The value of thedischarge capacity of the 50th cycle of Example 5 was similar to thevalue of Comparative Example 2. Based on the results above, the BETspecific surface area is preferably 2,000 m²/g or less and the porevolume is preferably 2.3 mL/g or less.

In all of Comparative Examples 5 to 8 where the carbon having thethree-dimensional network structure was used as the positive-electrodeactive material but the changing rate of the cross-sectional thicknessof the positive electrode film was 45% or greater, cycle service lifewas shortened. The reason for this was assumed that the connectionbetween materials constituting the electrodes was cut by the expansionand contraction of the electrode film when anions were intercalated tothe active material, and hence internal resistance was increased. Basedon the results above, it was found that the non-aqueous electrolyteelectricity-storage element, which utilized insertions of anions to thepositive electrode, maintained a high energy density, and had excellentcycle properties with inhibiting expansion of the positive electrode,was able to be provided.

For example, embodiments of the present disclosure are as follows.

<1> A non-aqueous electrolyte electricity-storage element including:a positive electrode including a positive-electrode active materialcapable of inserting and releasing anions;a negative electrode including a negative-electrode active materialcapable of inserting and releasing cations; anda non-aqueous electrolyte,wherein the positive-electrode active material is porous carbon havingpores having a three-dimensional network structure, and wherein achanging rate of a cross-sectional thickness of a positive electrodefilm including the positive-electrode active material defined by Formula(1) below is less than 45%

$\begin{matrix}{\begin{matrix}{{Changing}\mspace{14mu} {rate}\mspace{14mu} {of}} \\{{cross}\text{-}{sectional}\mspace{14mu} {thickness}\mspace{11mu} (\%)}\end{matrix} = {\frac{\begin{matrix}{{{Film}\mspace{14mu} {thickness}\mspace{14mu} {after}\mspace{14mu} {charge}\text{-}{discharge}} -} \\{{Film}\mspace{14mu} {thickness}\mspace{14mu} {before}\mspace{14mu} {charge}\text{-}{discharge}}\end{matrix}}{{Film}\mspace{14mu} {thickness}\mspace{14mu} {before}\mspace{14mu} {charge}\text{-}{discharge}} \times 100.}} & {{Formula}\mspace{14mu} (1)}\end{matrix}$

<2> The non-aqueous electrolyte electricity-storage element according to<1>,wherein the changing rate of the cross-sectional thickness is 20% orless.<3> The non-aqueous electrolyte electricity-storage element according to<1> or <2>,wherein a discharge capacity of the non-aqueous electrolyteelectricity-storage element under charge-discharge conditions of thenon-aqueous electrolyte electricity-storage element is 50 mAh/g orgreater but 140 mAh/g or less.<4> The non-aqueous electrolyte electricity-storage element according toany one of <1> to <3>,wherein a BET specific surface area of the porous carbon is 50 m²/g orgreater but 2,000 m²/g or less, and a pore volume of the porous carbonis 0.2 mL/g or greater but 2.3 mL/g or less.<5> The non-aqueous electrolyte electricity-storage element according toany one of <1> to <4>,wherein the pores of the three-dimensional network structure of theporous carbon are mesopores.<6> The non-aqueous electrolyte electricity-storage element according toany one of <1> to <5>,wherein the non-aqueous electrolyte is formed by dissolving a lithiumsalt in a non-aqueous solvent.<7> The non-aqueous electrolyte electricity-storage element according to<6>,wherein the non-aqueous solvent is at least one selected from the groupconsisting of dimethyl carbonate (DMC), ethylene carbonate (EC), andfluoroethylene carbonate (FEC).<8> The non-aqueous electrolyte electricity-storage element according to<6> or <7>, wherein the lithium salt is LiPF₆.

The non-aqueous electrolyte electricity-storage element according to anyone of <1> to <8> can solve the above-described various problems in theart and can achieve the object of the present disclosure.

1-8. (canceled)
 9. A porous carbon having connecting mesopores whichhave a three-dimensional network structure, wherein a changing rate of across-sectional thickness of an electrode film including the porouscarbon is less than 45%, wherein the changing rate of thecross-sectional thickness is measured by: mixing the porous carbon,acetylene black, an acrylate-based latex, and carboxymethyl cellulose ina mass ratio of the porous carbon, the acetylene black, theacrylate-based latex, and the carboxymethyl cellulose based on each ofsolid contents is 100:7.5:3.0:9.5, to obtain a mixture; adding water tothe mixture to obtain a slurry; applying the slurry onto one side of analuminum foil; drying the applied slurry; cutting the dried slurry intoa circle having a diameter of 16 mm to obtain the electrode film; andmeasuring the changing rate of the cross-sectional thickness defined byFormula (1), $\begin{matrix}{{\begin{matrix}{{Changing}\mspace{14mu} {rate}\mspace{14mu} {of}} \\{{cross}\text{-}{sectional}\mspace{14mu} {thickness}\mspace{11mu} (\%)}\end{matrix} = {\frac{\begin{matrix}{{{Film}\mspace{14mu} {thickness}\mspace{14mu} {after}\mspace{14mu} {charge}\text{-}{discharge}} -} \\{{Film}\mspace{14mu} {thickness}\mspace{14mu} {before}\mspace{14mu} {charge}\text{-}{discharge}}\end{matrix}}{{Film}\mspace{14mu} {thickness}\mspace{14mu} {before}\mspace{14mu} {charge}\text{-}{discharge}} \times 100}},} & {{Formula}\mspace{14mu} (1)}\end{matrix}$ wherein the charge-discharge in the Formula (1) is 50cycles charge-discharge where charge is performed with cut-off voltageof 4.5V and discharge is performed with cut-off voltage of 1.5V.
 10. Theporous carbon according to claim 9, wherein the changing rate of thecross-sectional thickness is 20% or less.
 11. The porous carbonaccording to claim 9, wherein the porous carbon is suitable for anon-aqueous electrolyte electricity-storage element, in which adischarge capacity of the non-aqueous electrolyte electricity-storageelement under charge-discharge conditions of the non-aqueous electrolyteelectricity-storage element is 50 mAh/g or greater but 140 mAh/g orless.
 12. The porous carbon according to claim 9, wherein a BET specificsurface area of the porous carbon is 50 m²/g or greater but 2,000 m²/gor less, and a pore volume of the porous carbon is 0.2 mL/g or greaterbut 2.3 mL/g or less.
 13. The porous carbon according to claim 9,wherein a BET specific surface area of the porous carbon is 800 m²/g orgreater but 1,800 m²/g or less, and a pore volume of the porous carbonis 0.2 mL/g or greater but 1.7 mL/g or less.
 14. The porous carbonaccording to claim 9, wherein a diameter of the mesopores is 2 nm orgreater but 50 nm or less.
 15. An electrode comprising an activematerial capable of inserting and releasing anions, the active materialbeing the porous carbon according to claim 9.